how to solve the linux timer error? - c

Question

#include <features.h>
#include <time.h>
#include <sys/time.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
typedef unsigned int uint32;
#define million 1000000L
long duration2ms, duration10ms, duration100ms;
double Task2ms_Raster, Task10ms_Raster, Task100ms_Raster;
timer_t firstTimerID, secondTimerID, thirdTimerID;
void TASK1(Task2ms_Raster) {
struct timespec start, stop;
int a, b, c;
uint32 StartTime, StopTime;
a=1, b=2, c=3;
if((StartTime = clock_gettime(CLOCK_REALTIME, &start)) == -1) {
perror("clock gettime");
}
a= b+c;
b = c+a;
c= a+b;
b = c+a;
c= a+b; a= b+c;
b = c+a;
c= a+b; a= b+c;
b = c+a;
c= a+b; a= b+c;
b = c+a;
c= a+b; a= b+c;
b = c+a;
c= a+b; a= b+c;
b = c+a;
c= a+b; a= b+c;
b = c+a;
c= a+b;
// I did several times like this.
printf("ETAS\n");
printf("ETAS1\n");
if((StopTime = clock_gettime( CLOCK_REALTIME, &stop)) == -1) {
perror("clock gettime");
}
duration2ms = (stop.tv_sec - start.tv_sec) +
(double)(stop.tv_nsec - start.tv_nsec) /
(double)million;
printf("time difference is= %ld\n", duration2ms);
}
void TASK2(Task10ms_Raster) {
struct timespec start, stop;
if(clock_gettime( CLOCK_REALTIME, &start) == -1) {
perror("clock gettime");
}
printf("ETAS2\n");
printf("ETAS3\n");
if(clock_gettime(CLOCK_REALTIME, &stop) == -1) {
perror("clock gettime");
}
duration10ms = (stop.tv_sec - start.tv_sec) +
(double)( stop.tv_nsec - start.tv_nsec) /
(double)million;
printf("time difference is= %ld\n", duration10ms);
}
void TASK3(Task100ms_Raster) {
struct timespec start, stop;
if(clock_gettime( CLOCK_REALTIME, &start) == -1) {
perror("clock gettime");
}
printf("ETAS4\n");
printf("ETAS5\n");
if((clock_gettime(CLOCK_REALTIME, &stop)) == -1) {
perror("clock gettime");
}
duration100ms = (stop.tv_sec - start.tv_sec) +
(double)(stop.tv_nsec - start.tv_nsec) /
(double)million;
printf( "time difference is= %ld\n", duration100ms );
}
static void timerHandler(int sig, siginfo_t *si, void *uc) {
timer_t *tidp;
tidp = si->si_value.sival_ptr;
if (*tidp == firstTimerID)
TASK1(Task2ms_Raster);
else if(*tidp == secondTimerID)
TASK2(Task10ms_Raster);
else if(*tidp == thirdTimerID)
TASK3(Task100ms_Raster);
}
static int makeTimer(char *name,
timer_t *timerID,
int expireMS,
int intervalMS) {
struct sigevent te;
struct itimerspec its;
struct sigaction sa;
int sigNo = SIGRTMIN;
/* Set up signal handler. */
sa.sa_flags = SA_SIGINFO;
sa.sa_sigaction = timerHandler;
sigemptyset(&sa.sa_mask);
if(sigaction(sigNo, &sa, NULL) == -1) {
perror("sigaction");
}
/* Set and enable alarm */
te.sigev_notify = SIGEV_SIGNAL;
te.sigev_signo = sigNo;
te.sigev_value.sival_ptr = timerID;
timer_create(CLOCK_REALTIME, &te, timerID);
its.it_interval.tv_sec = 0;
its.it_interval.tv_nsec = intervalMS * 1000000;
its.it_value.tv_sec = 0;
its.it_value.tv_nsec = expireMS * 1000000;
timer_settime(*timerID, 0, &its, NULL);
return 1;
}
int main(void) {
makeTimer("First Timer", &firstTimerID, 2, 2); //2ms
makeTimer("Second Timer", &secondTimerID, 10, 10); //10ms
makeTimer("Third Timer", &thirdTimerID, 100, 100); //100ms
while(1) {
sleep(100);
}
}
I created a timer to call the task for every 2ms, 10ms and 100ms. The tasks are just printing the value and calculating the start time and stop time for printing the value. when i run the above program, it is not displaying time difference between the start time and stop time (i.e duration2ms, duration 10ms nd duration100ms). could someone please help me.

Answer 1

The problem is that you don't save your timing values in TASK*() anywhere. This means clock_gettime() gets called twice in a row, having little or no time spent in between. What you should do is something along the lines of following:
#include <features.h>
#include <time.h>
#include <sys/time.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
typedef unsigned int uint32;
timer_t tmr;
struct timespec prev;
static void handle_timer(int sig, siginfo_t *si, void *uc) {
timer_t *tidp;
struct timespec current;
tidp = si->si_value.sival_ptr;
clock_gettime(CLOCK_REALTIME, &current);
printf("dif between calls to handle_timer: %ld\n",
current.tv_sec - prev.tv_sec);
prev = current;
}
int main(int argc, char **argv) {
struct sigevent se;
struct itimerspec its;
struct sigaction sa;
clock_gettime(CLOCK_REALTIME, &prev);
/* Set up signal handler. */
sa.sa_flags = SA_SIGINFO;
sa.sa_sigaction = handle_timer;
sigemptyset(&sa.sa_mask);
if (sigaction(SIGRTMIN, &sa, NULL) == -1)
perror("sigaction");
/* Set and enable alarm */
se.sigev_notify = SIGEV_SIGNAL;
se.sigev_signo = SIGRTMIN;
se.sigev_value.sival_ptr = &tmr;
timer_create(CLOCK_REALTIME, &se, &tmr);
its.it_interval.tv_sec = 1;
its.it_value.tv_sec = 1;
its.it_value.tv_nsec = 0;
timer_settime(&tmr, 0, &its, NULL);
while(1)
sleep(100);
return 0;
}
The difference here is that we're actually saving the time when handle_time() was called and then calculating the difference against the saved time.

Answer 2

The time difference is going to show zero in all cases because you are measuring the time it takes to print two lines, which is very fast. You are not timing the time between invocations of each task.
If you want to measure the time between invocations of the task, you need to preserve the time. As an example, I'll show one task:
void TASK3(Task100ms_Raster) {
static struct timespec start, stop = { .tv_sec = -1 }; // static duration!
if (stop.tv_sec < 0) {
(void) clock_gettime( CLOCK_REALTIME, &stop); // first time run
}
start = stop; // start from previous stop time
// do whatever here
(void) clock_gettime( CLOCK_REALTIME, &stop);
duration100ms = (stop.tv_sec - start.tv_sec)
+ (double)(stop.tv_nsec - start.tv_nsec)
/ (double)million;
printf( "time difference is= %ld\n", duration100ms );
}